Remote control for radio receivers



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J. K. KAHN ET AL REMOTE CONTROL FOR RADIO RECEIVERS Filed July 28, 19582 Sheets-Sheet 2 15y m M, )xe

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REMOTE CONTROL FOR RADIO RECEIVERS Filed July 28, 1938 2 Sheets-Sheet 1UNITED STATES PATENT OFFICE REMOTE CONTROL FOR RADIO RECEIVERS JacobKesner Kahn and Elmer G. Skoog, Chicago, Ill., assignors to Spiegel,Inc., Chicago, 111., a corporation of Delaware Application July 28,1938, Serial No. 221,672

8 Claims.

The present invention relates to the control of radio apparatus andparticularly to the remote control of radio receiving sets.

The control of a radio receiving set at a point remote from the set, aswell as at the set itself, has long been desired and is being utilizedmore and more. The control is relatively simple when only theenergization of the radio is controlled, because this necessitates onlythe exertion of control over the power supply. However, when it isdesired to control also the volume and the tuning both at the set and ata point remote therefrom, the controls become considerably morecomplicated and give rise to difficulties that have not heretofore beensurmounted except by the use of complicated or expensive mechanicalequipment.

One of the primary difficulties results from attempts to control thevolume from a distance. When this control is efl'ected throughconductors extending from the remote point to a control grid of theamplifier, unstable and noisy operation results because of the excessivelength of the grid connection. Attempts have been made to overcome theaforementioned difliculty by the use of combined electrical andmechanical means, but, because of the resulting increase in initialcost, the increased probability of service dimculties, etc., these havenot found a widespread use. For example, remote volume control has beenattempted through the use of variable resistances in the grid circuitcontrolled from a distance through a pawl and ratchet mechanism orreversible motor. Attempts have likewise been made to control the volumethrough mechanical means alone, as through the use of flexible shaftsand the like, but these arrangements are expensive and also give rise tomechanical difiiculties. The difficulties mentioned above are presenteven when the distance between the control element and the amplifier arerelatively close, as in an automobile, where a flexible shaft has beenused with but indifferent success.

It is the primary object of the present invention to provide a remotevolume control for radio apparatus that is relatively inexpensive,easily installed, free from mechanical difilculties, and which does notdeleteriously affect the operation of the apparatus.

A further object of the invention is to provide a remote volume controlcomprising a remotely controlled light source that is electricallyindependent of an impedance element associated with the radio apparatuswhereby the volume may be controlled from a remote point simply bycontrolling the intensity of the light source.

A more specific object of the invention is to provide a remote volumecontrol for radio receiving apparatus which comprises a photoelectricimpedance element in circuit with and located in proximity to suitableelements of the apparatus, the value of which is selectively varied bycontrolling the intensity of a light source associated therewith from apoint remote from the apparatus.

Another object of the invention is to provide a simplified control forradio receiving sets whereby the energization, volume, and tuning may becontrolled from a. point remote from the set.

A still further object of the invention is to provide a radio receivingset and a remote control unit therefor so constructed that the set maybe operated either in the ordinary manner by controls constructed as aunit therewith, or from a remote point by means of the control unit,which is arranged to be plugged into a suitable receptacle convenientlymounted upon the set.

Another object of the invention is to provide a radio receiving set ofthe type described with a selector switch whereby the circuitconnections may be controlled to condition the receiver for control fromeither the set or the remote point.

A further object of the invention is the provision of a remote volumecontrol which can be merchandised as a separate and optional unit, whichcan be readily installed in new or existing radio sets by a layman, andwhich involves a minimum disturbance of electrical circuits in the sets.

Other objects and advantages of the present invention will become moreapparent from the ensuing description in the course of which referenceis had to the accompanying drawings, in

which:

Fig. 1 is a diagrammatic representation of a radio receiving setembodying the present invention;

Fig. 1A is a diagrammatic view of the wiring of a remote control unit,the wiring being a continuation of that shown in Fig. 1;

Fig. 2 is a schematic representation of the invention applied to a radioreceiving set, the remote control unit being illustrated in a. roomseparate from the one in which the set is located; and

Fig. 3 is a partial perspective view of the rear of a radio receivingset illustrating the manner in which the amplifier control unit and thecontrol conductors are attached to the chassis of the receiving set.

In brief, the present invention consists in the utilization of aphotoelectric cell in suitable circuit arrangement with the amplifier ofthe receiving set and adapted to be influenced by an electricallyenergized light source which is in turn controlled by means of arheostat forming part of a remote control unit.

The present invention, in its broader aspects, is adapted to be usedwith various types of radio receiving sets but, in order better toillustrate its advantages, it has been illustrated in conjunction with aradio receiving set provided with many of the more recent improvements.For instance, while the invention has been illustrated in connectionwith a radio receiving set provided with an automatic volume control, itmay be used quite independently thereof.

Before proceeding with the detailed description of the circuitarrangement, it may be well to outline the invention generally. Ifreference is had particularly to Fig. 2, it may be noted that thereference numeral 2 illustrates a radio receiving set provided with theusual dial 9 and adapted to be supplied with power through the insulatedconductor 4 connected to an outlet. From the ensuing description of theinvention, it will be noted that the outlet is connected to a suitablesource of 110 volt alternating current.

The receiving set is further illustrated as being of the type havingelectric push button tuning, the various stations being selected bymeans of a plurality of push button switches 5, each switch beingassociated with a predetermined station. The receiving set is providedwith the usual power and volume control switch 6, a tone control I, amanual station selector 8, and a band switch 9. In addition to theseappurtenances the receiving set is provided with a two-positionswitch'by means of which the receiving set may be selectivelyconditioned for local or remote control, this switch being indicated byreference numeral I0.

When the selector switch is operated to condition the receiving set forcontrol from a remote point, the set may be controlled from a controlunit II which may be located at a substantial distance from the set. InFig. 2 the control unit has been illustrated as being located in a roomother than the one in which the set is located, the two rooms beingseparated by a partition l2. The remote control unit is connected to thereceiving set by a plural conductor cable 13, the cable being maderelatively flat in order that it may be run along the floor withouttaking up too much space.

I The remote control unit II is provided with a plurality of push buttonswitches ll corresponding to similar switches 5 on the set proper andwith a volume control switch I5 and a power switch It. These controlsare so arranged with the controls on the receiving set that either theformer or the latter may be rendered effective upon proper operation ofthe selector switch l0. While illustrated as being separate, the volumecontrol switch l5 and power switch l6 may be combined to form a singleunit.

To enable the remote control to be applied to a receiving set which ispreferably built ready to receive it, the various conductors comprisingcable l3 are all connected to an elongated flexible plug I'I adapted tobe plugged into a suitable receptacle l9 mounted upon the chassis I9 ofthe receiving set, as illustrated in Fig. 3. Upon reference to thisfigure it may be noted that the usual tubes and controls of the set havenot been illustrated. It is believed those skilled in the art willappreciate that the chassis I9 may be of any usual construction and maybe modified as indicated for the reception of the plug H.

The chassis I9 is also provided with a receptacle 20 so as to receiveanother plug-in type unit 2| which includes the light source 22 and thelight responsive photoelectric cell 23 adapted to be influenced thereby,and forming part of the heart of the present invention. Thephotoelectric cell and light are both removably mounted upon sockets sothat they may be replaced when necessary. The receptacles in which theplug-in units l1 and 2| are mounted have their various terminals soconnected that, with the selector switch Ill in its remote controlposition and the plug-in units in place, the photoelectric cell isconnected in circuit with the ampliiier of the receiving set and sothat, as the intensity of the light emanating from the lamp is varied,the volume of the receiving set is varied. The arrangement, as willappear more fully from the detailed description about to follow, is suchthat the remote control unit and the conductors connecting it to thereceiving set are electrically independent of the amplifier circuit,thereby to eliminate the effect of any electrical disturbances uponeither the remote control or the conductors.

From the wiring diagram of the receiving set, shown in detail in Fig. 1,those skilled in the art will recognize that it is a multi-rangesuperheterodyne receiver adapted to be energized from the usual 60cycle, 110 volt alternating current source through the conductors 4 andthe power supply switch 24 which has been illustrated in Fig. 1, forpurpose of clarity, as separate from the volume control switch 6 of Fig.2. However, it should be understood that switches 6 and 24 may be andusually are combined in one unit. Further details of the power supplyproper will be described hereinafter.

The multi-range superheterodyne receiver comprises an antenna circuit 25connected to a radio frequency selector switch 26 illustrated in contactwith a conductor 21 leading to a coupling circuit 28 tuned to conditionthe receiver for reception on the standard broadcast band. The switch 26is adapted to be actuated simultaneously with switches 29, 30, and 3|,which, together with switch 26, constitute the previously described bandswitch 9 of Fig. 2, and like switch 26 are shown in positionsconditioning the set for reception on the standard broadcast band. Therange selector switch controls, in customary manner, the circuits of theusual mixer tube 92 (type R. C. A.-6A8), and the local oscillator tube33 (type R. C. A.-6J7). Switch 29 has a pair of contacts 29A and 293,the latter serving also as a control for the electric tuning, it beingso arranged and constructed that electric tuning is obtainable only onthe standard broadcast band.

The receiving set may be tuned by means of three condensers 34, 35 and36 joined together for operation as a unit, either manually by the knob8 in the usual manner, or by an electric motor 31 comprising part of theelectric tunin means. The position of the condensers may be controlledby the motor, in accordance with the present invention, either from thereceiving set itself or from a remote point, all as will appear shortly.

The receiving set comprises two stages of intermediate frequencyamplification. The output of the mixer tube 32 is coupled to the firststage intermediate frequency amplifier comprising the tube 38 (type R.C. A.-6K'7) through a tuned transformer 39. The output of the tube 38 iscoupled through a tuned transformer 40 to the input of the second stageintermediate frequency amplifier which comprises the tube 4| (type R. C.A.-6K7).

The output of the second stage intermediate frequency amplifier tube 4|is coupled through a tuned discriminator transformer 42 to a pair ofthree element vacuum tubes 43 and 44 (both of type R. C. A.-6J5). Thetubes 43 and 44 perform the dual functions of a detector and a source ofautomatic gain control. The automatic gain or volume control biaspotential is applied in conventional manner to the mixer tube 32 and thefirst stage intermediate frequency amplifier tube 38 through a conductor45, the bias potential itself being derived from the voltage dropobtained in usual manner from a resistance network indicated generallyby reference numeral 46.

The audio frequency output of the detector tube 43 is impressed across avolume control resistor 41, which has a value of approximately onemegohm in accordance with usual practice. The connection of the detectoroutput to the resistor 41 is effected by a conductor 50 havinginterposed therein a condenser 5| and a switch blade 52 of thetwo-position multi-blade selector switch ID mentioned previously in thedescription of Fig. 2. The selector switch is illustrated in theposition it occupies when conditioning the receiver for control from theset. In this position the opposite end of the resistor 41 is groundedthrough another blade 54 of the selector switch.

The volume of the receiving set is controlled in conventional manner bymeans of a potentiometer connection 55 (which may be made, as

indicated above, a part of the combined volume and power control unit 6)leading to the upper one of two contacts associated with a third switchblade 56 of the selector switch. The connection is movable to the leftto increase the volume and to the right to decrease it, in accordancewith standard practice. Blade 56 is connected by a conductor 51 to thegrid of a three-element audio frequency amplifier tube 58 (type R. C.A.-6J5).

The receiving set is also provided with the usual tone control indicatedgenerally by reference numeral 59 and including a contact 50 movable byknob 1. The tone control is connected by conductor 6|, a blade 62 of theselector switch and conductor G3 to the volume control resistor 41 andby conductor 64 to the plate of tube 58. The second stage of audiofrequency amplification is provided by a pair of vacuum tubes 65, 66connected in push-pull relationship. The first pushpull tube 65 isdriven by the amplifier tube 58, and the second is driven through aphase reversing tube 61. This is a well-known method of supplying thesecond tube of a push-pull power amplifier with a voltage equal to, butopposite in phase to the exciting voltage of the first tube.

The output of the push-pull amplifier is connected to an outputtransformer 68, which is in turn connected to a loud speaker unitindicated by reference numeral 69.

The receiving unit per se is supplied with power from the alternatingcurrent source through the Examiner customary power pack comprising atransformer 10, a full-wave rectifier 1| of the vacuum tube type, and afilter 12. The transformer consists of a primary winding 13 and foursecondary windings 14 to 11, inclusive. The secondary winding 5 14supplies a suitable potential to the filamentary cathode of tube 1|(type R. C. A.-5Z3) and the secondary winding 15 supplies suitable anodepotentials to that tube. The secondary winding 15 serves as a source oflow voltage current for the cathode heaters of the various tubes of thereceiving set. One side of the secondary winding is grounded throughconductor 18 and the other is connected by a conductor 19 to the variouscathode heaters.

The secondary winding 16 also serves as a low potential source forenergization of the light source 22 of the remote control, while thesecondary winding 11 serves as a source of potential for the reversibletuning motor 35. The de- 20 tails of the remote control and electrictuning means will be discussed hereinafter after the completion of thedescription of the power supply. The rectified and filtered directcurrent output of the power pack is connected to the receiving 25 setproper through leads 83 and 84 the former leading to the anode circuitsof the first stage audio frequency amplifier and the phase reversingtubes 58 and 61, and the latter through a branch conductor 85, to theanode and screengrid circuits of the other tubes, all in accordance withwell-known principles.

The particular construction of the electric tuning means is not ofparticular moment, except that it should be of a type adapted to providea dual control, 1. e., from a point remote from the set and from the setitself. In the illustrated embodiment the tuning means is of a typewellknown in the art, which has been modified in such manner that it maybe operated at a point remote from the receiver and conjointly with theremote volume control thatforms the primary feature of the presentinvention. The modification of the tuning control for its presentpurpose and the association thereof with the particular remote volumecontrol to be described forms an ancillary feature of the invention.

The electrical tuning means, illustrated for greater partdiagrammatically only, comprises the previously mentioned reversiblemotor 31 which may be of the single phase shaded pole type adapted todrive a commutator 9| and the ganged tuning condensers through a clutch92. The commutator comprises a pair of substantially semicircularsegment contacts 9|A and 9|B through one or the other of which the mainmotor winding 31A and either of the auxiliary windings 31B and 31C maybe energized to effect rotation of the condensers to predeterminedpositions. The commutator is, according to usual custom, rotatabledirectly with the condensers so that its angular position with respectto the condensers is fixed. The motor shaft is normally disengaged fromthe tuning condensers and commutator, but engages the latter whenenergized (the engagement may 65 be effected by so constructing themotor that its rotor is moved axially when it is energized).

In order to eliminate undesirable sounds during rotation of thecondensers, there is provided a silencing switch 93 adapted to be closedwhen 70 the motor is energized. When the switch is closed the volumecontrol resistor 41 is short-circuited by connecting both ends thereofto ground. One end of the resistor, it may be remembered, is normallyconnected to ground through selector switch 75 blade 54 and when switch92 is actuated, the pposite end thereof is connected to ground through acircuit including the conductors 94, 95 and 96.

The selective energization of the motor is controlled by one of thestation selector push-button switches and a master push-button switchIOI, which together constitute what may be termed local tuning control,inasmuch as it is built as a component part of the receiving set. Thislocal tuning control may be of any well-known type and, although theconstruction of the switches 5 have not been illustrated in detail, theyare of the type adapted to remain in a depressed position when pushedin, and, furthermore, are so arranged that when one is depressed, theothers are released. However, for the purpose of illustrating theoperation of the present invention, the switches 5 have been illustratedas being biased into their uppermost position by means of springs, andthe switch IOI has been illustrated as of the type which must beactuated from either one of its positions to the other.

The master push-button switch IOI also serves as a means for selectingeither manual or electric tuning. When manual control is desired, theswitch must be operated to its depressed position-its normal positionand the position in which it is illustrated. In this position it isconnected to the conductor I02 leading to the silencing switch for apurpose that will be described more fully hereinafter. When electrictuning is desired, the switch is actuated into its uppermost position.In this position the switch is adapted to condition the motor 31 forenergization upon closure of any one of switches 5.

The tuning motor is supplied with energy from the transformer secondarywinding 11, through a circuit including, in part, a conductor I03, 9.thermal-responsive switch I04, the main motor winding 31A, either ofwindings 313 or 31C, depending upon the position of the commutatorsegments when one of the switches 5 is pushed in, either commutatorsegment 9 IA or 9 I B, a predetermined one of the plurality ofconductors I05 and branch conductors I06, which lead to the push-buttonelectric switches 5. When the master push-button switch IOI is in itsuppermost position, it completes the connection of one side of thesecondary winding 11 to ground through conductor I08 and a switch bladeI09 that is ganged for operation with the selector switch I0 I. Whenswitch blade IOI has been actuated as indicated, the motor energizingcircuit is completed through a predetermined one of the push-buttonswitches 5, a branch conductor III connecting the push-button switchesin series, and a conductor II2 leading from the push-button switch 5 atthe extreme left of Fig. 1 to a conductor H3 connected to ground throughthe switch segment 293. Thus, electric tuning is possible whenever theswitch IN is in its uppermost position and the range selector switch isoperated to condition the receiving set for reception on the standardbroadcast band. The depression of any one of switch blades 5 completesan energizing circuit to the motor 31 through the described conductorsand either commutator 9 IA or 8 IB. Once energized, the motor operatesuntil the commutator is rotated to a point in which the circuit isbroken by the break between the two segments 8 IA and 9 IB.

It should be understood that the above described receiving set proper,which, it may be remembered, is well known to those skilled in the art,may be modified by addition of features other than those described andalso by omission of some described. It is possible to realize theadvantages accruing from the use of the present invention in many andvaried types of receiving sets as will appear shortly from the detaileddescription of the invention.

The present invention, which was described briefly previously, isdirected particularly to the control of radio receiving sets from apoint remote from the set. In some cases the remote point may be at aconsiderable distance from the set, as where the remote control isexercised from a different room from that in which the set is located,or relatively near the set, as in the case of an automobile radio. Somefeatures of the invention are capable of even wider use than that justindicated.

The remote control of the present invention is particularly advantageousin that it can be sold independently of the receiving set. The receivingset is manufactured and sold ready to receive the remote control, sothat if the purchaser desires the remote control either at the time ofthe purchase or subsequently, it can be installed with ease. One of thefeatures of the invention resides in its simplicity and the attendanteconomical manufacture, whereby the cost of the receiving set, eitherwith or without the remote control is not appreciably increased.

The control of the present invention comprises the previously describedlight source, the photoelectric cell in circuit with and located inproximity to the receiver amplifier, and the remote control unit. Thelatter is provided with means for electrically tuning the receiving set,and volume and power control means.

Electric tuning at the remote station is accomplished by means of thestation selector push button switches I4 connected in parallel to thepush button switches 5 by extensions of the branch conductors I06. Theenergizing circuit for the motor 31 is adapted to be completed byselective closure of the push button switches I4, which correspond, bothin construction and arrangement, to the switches 5. In their normalpositions the switches I4 are all connected in series by the conductorsI23 and they are all connected to ground through the branch conductorH2. The remote control unit is also provided with a master push-buttonswitch I24, corresponding to switch IN and adapted in its normalposition to complete a circuit to the extension of conductor I02.

The control circuits are so arranged that the selector switch I0 has tobe actuated into its displaced or remote control position before thevolume and tuning controls at the remote point can be used to controlthe set. This operation is made possible by the switch blade I09 throughwhich one side of the tuning motor energizing circuit is connected toground. With the selector switch and blade I09 in their normalpositions, the master push-button switch I24 at the remote control unitcannot complete the ground circuit. However, when the selector switch isin its displaced position, depression of switch I24 completes a circuitto ground through conductors I29 and I3I and switch I09.

The supply of power to the receiving set is controlled at the remotecontrol unit by means of the power control switch I6 connected inparallel with the local power control switch 24 by a pair of conductorsIN.

The remote volume control, which forms a primary feature of the presentinvention, comprises the previously mentioned light source 22 andphotoelectric cell 23, the latter constituting a control element whoseimpedance varies in response to the intensity of the light source. Thephotoelectric cell is connected in circuit with a plurality of resistorsI36 to I39, inclusive, and a condenser I4II which are adaptedselectively to be placed in the amplifier circuit with the cell in suchmanner that the volume may be controlled from the remote control unitsimply by varying the intensity of the light source.

When the selector switch III is operated to its displaced position, theswitch blade 52 connects the resistors I36 to I39 to the output of thedetector tube 44 in place of resistor 41. At the same time thepotentiometer lead 55 is disconnected from conductor 51 and the latteris connected by switch 56 to a conductor I4I leading to the junction ofresistors I31 and I38. The switch blade 62 disconnects conductors GI and63 and connects the former to a conductor I42 leading to the junction ofresistors I36 and I31. Switch blade 54 grounds resistor I39, therebycompleting the connection of the series connected resistors I38 to I39,inclusive, in the amplifier circuit in place of the resistor 41.

The photoelectric cell 23 is adapted to be activated from a source ofdirect current potential having a value in proximity to volts. In thepresent embodiment this potential supply is obtained from the plateconnection I43 of the phase reversing tube 61 which is adapted to beconnected to the anode of the photoelectric cell by conductors I44 andI45 and a switch I46. The cathode of the photoelectric cell is connectedby a conductor I41 to the junction of resistors I38 and I39 whereby thepotential applied to this point from the 90 volt source may be varied bycontrolling the value of the impedance of the photoelectric cell.Variation of this potential in turn effects a change in the potential ofthe grid of the first stage audio amplifier tube 58 and a change involume.

Energy is supplied to the light source 22 from the secondary winding 16of transformer 10 under the control of the selector switch I0 and thevolume control rheostat I5 forming part of the remote control unit. Thissupply circuit extends from the secondary winding 16 through conductorI52, switch blade I53 and conductor I54 to the rheostat I5 and from thelatter directly through conductor I55 to one terminal of the lightsource 22. The other terminal of the light source is grounded at I56.

Prior to describing the operation of the remote control in detail, itmight be well to review briefly the operation of the receiver itself.Assuming that the switches are all in the positions indicated, the setis conditioned for manual control at the receiving set. When the powersupply switch 24 is closed, the transformer 10 is energized and power issupplied to the radio receiving set. With the range selector and controlselector switches in the positions indicated, the set is conditioned forreception on the standard broadcast band and reception will be had onthe frequency corresponding to the station last tuned in. At this timeconductors I02 and H3 are connected to ground, the former establishing aground connection for the receiver and the latter conditioning theelectric tuning for operation upon proper actuation of the selectorswitch I0. Other stations may be tuned in in accordance with usualpractice by manually operating the ganged tuning condensers, and thevolume may be controlled ation of the impedance of the cell to apply aExaminer in customary manner by operation of the potentiometer 55.

When it is desired to utilize electric tuning and I to tune in thevarious stations at the receiving set, the master push-button switchIIII is oper- 5 ated to its uppermost position, thereby grounding oneside of the secondary winding 11 through the electric switch blade I09,as previously described. This conditions motor 31 for energize.- tionupon the depression of any one of the station selector push-buttonswitches 5. The selected switch 5 is maintained in its depressedposition until the motor 31 stops rotating, which occurs when thecircuit thereto is broken at the break between the segments of thecommutator. The radio is silenced during energization of the tuningmotor by actuation of the switch 93, which, as previously described,acts to short-circuit the volume control resistor 41.

When it is desired to tune in some other station another push-buttonswitch 5 corresponding to the desired station is depressed and the motor31 again energized to operate the tuning condensers to a predeterminedposition.

When it is desired to control the operation of 25 the receiving set fromthe remote control unit, it is necessary only to actuate the selectorswitch III to its displaced position, in which the light controlledvolume control means is rendered effective. When the switch is sodisplaced, the supply of power to the receiving set may be controlledfrom the remote unit by means of the power switch I5. When the latter isclosed, energy is supplied to the primary winding of the transformer 10.Energy is also supplied to the light source 22 whenever the selectorswitch I0 is operated to its displaced position. -This results from thefact that upon such actuation switch I53 connects the light source inseries with the volume control rheostat I5 across the secondary winding16 of the transformer. The intensity of the light source is controlledby the position of the movable arm of the rheostat and, since theimpedance of the photoelectric cell is dependent upon and varies withthe intensity of the light directed upon it, the volume of the receivingset can be varied by utilization of the varivariable potential to thejunction of resistors I38 and I39. Variation of this potential resultsin a variation of the bias of the control grid of the amplifier tube 58to effect a change in volume.

The described arrangement of the photoelectric cell in circuit with theseries connected resistor is such that the higher the impedance of thecell, the greater the volume of the receiver. This results from the factthat the photoelectric cell is connected in parallel with the resistanceI39 and the grid of the first stage amplifier tube 58 is connected tothe junction of resistances I31 and I38 through the switch 58 andconductor 51. Consequently, when it is desired to increase the volume,it is necessary to decrease the intensity of the light source SI, andwhen it isdesired to decrease the volume, it is necessary to increasethe intensity of the light source. In other words, the volume isdirectly proportional to the impedance of the cell, i. e., the greaterthe volume the greater the impedance and, the less the volume the lessthe impedance. Since the impedance of the cell is inversely proportionalto the intensity of the light source, the maximum volume is obtainedwhen the light intensity is at its minimum and vice versa. However, theadvantages of the 7 present invention could be realized from a circuitarrangement in which the response of the volume in response to changesin cell Impedance and light intensity is reversed.

In actual practice diiierent types of light sources and photoelectriccells have been used. Excellent results have been obtained by using a 6volt, 32 candle power Mazda lamp as the light source and an R. C. A. No.923 photoelectric cell. The values of the resistors I35 to I39 may bevaried to obtain the desired range of volume attenuation. A very widerange of attenuation has been obtained by making these resistors withresistance values of /5 and 1 megohm, respectively. These values aregiven only for illustration and are not intended to limit the inventionin any manner. The condenser I40 has a value of .25 microfarad and isprovided for the purpose of eliminating a slight hum that occurred withthe lamp and photoelectric cell disconnected and the selector switch II) in its remote control position. If the total resistance of the seriesconnected resistors is decreased to too small a value, a satisfactoryminimum volume cannot be obtained and, likewise, if increased unduly themaximum volume obtainable is not satisfactory.

The response of the volume to changes in light intensity issubstantially immediate. The connection of the light source to analternating current supply does not produce, as might be supposed, anyhum in the set. It appears that the light source has sufllcient inertiaso that the light intensity is not varied because of the use ofalternating current as the source of heat. The operation of the controlis substantially the same when the lamp is connected to a source ofdirect current, as a storage battery. The lamp may be connected directlyto the 110 volt supply, if desired.

Likewise, no hum results from the fact that the anode of thephotoelectric cell is connected to the plate circuit of one of the tubescomprising the push-pull amplifier. There is a slight variation in thevoltage supplied to the cell, particularly when the set is first turnedon, but this has no deleterious effect upon the operation.

When it is desired to tune in the various stations from the remotestation, it is necessary only to actuate the master push-button switchI24 to its displaced position, thereby interconnecting conductors I29and ISI. This interconnection completes the connection of conductor I08to ground through the switch I09, which it may be remembered, wasactuated to, its displaced position upon actuation of the selectorswitch III. Thereafter, the desired station may be tuned in merely bymaintaining the desired selector push-button switch I4 in its depressedposition.

The circuit arrangement is such that the radio is silenced when thetuning motor 31 is energized from the remote control unit. This resultsfrom the fact that theseries connected resistors I 36 to I39 areshort-circuited by means of the switch 93 in a manner identical to theshortcircuiting of the volume. control resistor 41. The describedarrangement, furthermore, has the advantage that the automatic volumecontrol is eflective to control the volume of the receiving set wheneither the local or remote tuning is used.

It should be noted that the selector switch III has not been illustratedas controlling the power supply circuit and, consequently, the receivercan be energized by either of power switches 24 or I6. If desired, asingle pole switch could be interposed in circuit with one of conductorsI33 to control that circuit. This switch could be made part of selectorswitch II) and so arranged that the power supply could not be controlledfrom the remote control unit except when switch III is in its displacedposition.

The particular embodiment that has been described above, may be modifiedto adapt it for use with various types of receivers, and it should notbe considered .as restricting the invention in any manner.

- What we claim as new and desire to secure by Letters Patent is:

1. In apparatus of the type described the combination including, anamplifier of the type including a vacuum tube, means including amanually operable potentiometer in proximity to said amplifier forcontrolling the bias applied to a control electrode of said tube forcontrolling the volume of the amplifier, means for controlling thevolume of said amplifier from a point remote from the amplifier, saidlast mentioned means including a fixed resistance located in proximityto said amplifier and adapted to be connected to said control electrode,a light controlled impedance element in circuit with said resistance forvarying the bias applied to said electrode, a light source influencingsaid element and a rheostat remote from said amplifier for controllingthe intensity of the light source, and selectively operable means forrendering either of said volume controlling means operable.

2. In combination, a radio receiving set comprising an amplifier of thevacuum tube type, means including a resistor in circuit with theamplifier and a potentiometer connection leading therefrom to a controlelectrode of a vacuum tube for controlling the volume of the amplifierat the set, means for controlling the volume of said amplifier from apoint remote from the set, said means including a resistor, aphotoelectric cell connected to said resistor, a source of potential forsaid cell, alight source, the intensity of which is variable from theremote point for influencing said cell and a source of energy for saidlight source, and means for selectively rendering said volume controlmeans eilective, said last mentioned means comprising a multi-poleselector switch so constructed and arranged in circuit with both saidvolume control means, that when the remote volume control is selected,the control electrode of the vacuum tube is connected to a fixed pointof said second mentioned resistor and the photoelectric cell and lightsource are connected to their associated energy sources.

3. In combination, a radio receiving set comprising an amplifier of thevacuum tube type mounted within a suitable cabinet, means including aresistor in circuit with the amplifier and a potentiometer connectionleading therefrom to a control electrode for controlling the volume ofthe amplifier at the set, tone control means including a secondconnection to said resistor, means for controlling the volume of saidamplifier from a point remote from the set, said means including aresistor, a photoelectric cell connected to said resistor, a source ofenergy for said cell, a light source adapted to influence said cell,means for varying the intensity of said light source from the remotepoint and a source of energy for said light source, and means forselectively rendering said volume control means effective, said lastmentioned means comprising a multi-pole selector switch so constructedand arranged in circuit with both said volume control means and the tonecontrol means, that when the remote control means is selected, thecontrol electrode of the vacuum tube and the tone control connection areconnected to fixed points upon the resistor and the photoelectric celland light source are connected to their associated energy sources.

4. In an amplifier system, the combination including, an amplifier ofthe type employing a vacuum tube comprising an anode, a cathode and acontrol electrode, means including a resistance having one terminalgrounded and the other connected to a signal producing means and aconnection intermediate the terminals leading to the control electrodefor applying the signal to said amplifier, means including a connectionfrom a point intermediate the ungrounded terminals and the saidintermediate connection providing a tone control for said amplifier, andmeans for varying the bias potential applied to the control electrodethereby to vary the volume of the amplifier, said means including asource of bias potential, a light responsive variable impedanceconnecting said source to said resistance between the grounded terminaland the said intermediate connection, and a light source for influencingsaid impedance.

5. In combination, a radio receiving set comprising a detector stage andan amplifier stage, said amplifier stage being provided with a volumecontrol comprising a resistor connected to the detector stage and amanually variable connection therefrom to a control electrode of a tubeof the amplifier stage, a plural position selector switch built into theset for controlling the connections of said resistor to said detectorstage and the control electrode to said variable connection, a socketbuilt into the set to receive a second volume controlling means, asecond socket built into the set to receive conductors forming part of aremote control unit for said second volume controlling means, andcircuit connections controlled by said selector switch whereby thevolume of the amplifier may be controlled from the remote control unitupon operation of the selector switch into one of its positions and thesecond volume controlling means and the conductors are placed into theirrespective sockets.

6. In combination, a radio receiving set comprising detector andamplifier stages of the vacuum tube type mounted upon a chassissupported by a cabinet, said stages being interconnected by apotentiometer whereby the volume of the receiving set may be varied, asource of power supply for the receiving set, a two-position selectorswitch adapted in one of its positions to connect said potentiometer incircuit between the detector and amplifier stages and in the other todisconnect said potentiometer, sockets built into the chassis to receivea photoelectric cell and light, a third socket built into the set, andmeans including circuit connections between said sockets, selectorswitch, amplifier, and the power supply whereby the volume of thereceiving set may be controlled by a remote control unit upon operationof the selector switch into its other position and placing the cell andlight into their associated sockets and connecting the control unit tothe third socket.

7. In a radio receiving set of the type comprising achassis, anamplifier mounted thereon and a volume control at the set, a selectorswitch, a socket built into the chassis to receive a photoelectric celland a lamp, a socket built into the chassis to receive a remote volumecontrol unit connector, and means including circuit connections betweenthe switch, amplifier and sockets whereby upon operation of the selectorswitch into a predetermined position and the cell, lamp and connectorare inserted into their respective sockets, the remote volume controlunit is rendered efiective and the first mentioned volume controlineffective.

8. In combination, a radio receiving set comprising means for tuning theset for reception at difierent frequencies, manually operable means atthe set for operating said tuning means, means including a set ofswitches at the set and a second set at a point remote therefrom andelectrical means controlled thereby adapted to control said tuning meansfor conditioning said set for reception at predetermined frequencies, a.control switch at the set and a second control switch at the remotepoint, each of said switches being operable into a predeterminedposition to render said last mentioned means efiective, and a selectormeans at the set for rendering the control switch at the set or theremote point operative to control said tuning control means.

JACOB KESNER KAHN. ELMER G. SKOOG.

